The documentation for the fr_timer_avp/fr_inv_timer_avp modparams of TM say:
This parameter is kept for backwards compatibility (hence its value expressed in seconds instead of milliseconds and its arcane way of specifying the avps). The recommended replacement is using t_set_fr() on a per transaction basis.
The problem is that, as far as I can see, t_set_fr() does not accept PV arguments, so it is not a replacement except in cases where these values are hard-coded.